Quote Originally Posted by PeteS View Post
I keep coming back to the chain with this Cav Bordeaux sprint. If it's jumping between 11 and 12, then it's a badly adjusted derailleur but from what Ralf Aldag has implied, it was a chain issue?
The modern fashion for using the big ring and large rear sprockets means that the chain tension will always be a little bit slack when using the smallest sprockets. Add to this the fact that when sprinting at maximum power, which can exceed 1000W for the biggest sprinters, it is a case of stomping on the pedals in a piston like action, which results in huge tension on the chain followed, briefly, by very little. It does ask a lot of the chain, and the slightest bump at the wrong time is likely to jump the chain.

A very long way down the talent levels, I once unshipped the chain whilst standing up and sprinting on the smallest sprocket (a 13) at over 30mph. Hitting neutral, as the chain went between the smallest sprocket and the frame is pretty scary, but probably everyone who's sprinted at maximum power on the road has done it at least once. I checked the bike afterwards, and it was correctly adjusted so in theory it wasn't possible. But it happened.